The demise of the dinosaurs found recorded in ancient mollusks

Researchers discover evidence of a one-two punch of climate change.

One of the ancient mollusks analyzed by researchers to determine the temperature of the Antarctic ocean some 65-70 million years ago.
(Photo: Sierra Petersen)

For more than 135 million years, dinosaurs of various sizes and species ruled both land and sea. In a moment akin to a geological blink, they were gone; wiped out by a comet, a meteorite, a global volcanic eruption, or some other unknown force.

A new study from researchers at the University of Florida and the University of Michigan is giving credence to the idea that a closely-occurring combination of cataclysms, or extinction pulses, may have been responsible for first crippling and the subsequently finishing off the age of the dinosaurs.

In a remarkable breakthrough, the teams discovered this correlation not in the geological record, but by studying ancient ocean data preserved in the shells of ancient mollusks. The 29 specimens, which lived between 65.5 to 69 million years ago in a shallow sea off the Antarctic Peninsula, contain varying isotopic compositions of oxygen and carbon in their shells. Using a new tool called "clumped isotope paleothermometry," the team was able to reconstruct ocean temperatures based on how the isotopes settled as the shells grew.

A few of the 29 ancient mollusks used by the researchers to plot average ocean temperatures over 3.5 million years. (Photo: Sierra Petersen)

For instance, based on the data, were you to dip your toes into the waters off the Northern Antarctica Peninsula some 70 million years ago, the average temperature would have been a refreshingly chilly 46 degrees Fahrenheit. Within this average, the researchers discovered two notable temperature spikes that seemingly coincide with the estimated dates of two cataclysmic events on Earth.

The first, which saw a jump in Antarctic ocean temperatures as high as 14 degrees Fahrenheit occurred roughly around the same time as the formation of the Deccan Traps. The Deccan, located in India, is one of the world's largest volcanic features. During their creation at the end of the Cretaceous, the lava flows were so large that they covered an area half the size of India, or nearly 600,000 square miles.

It's estimated that the massive amounts of atmospheric CO2 released by the Deccan Traps resulted in a dramatic warming of the planet that wiped out several species and crippled many more. According to the second temperature spike recorded in the mollusk shells, those remnants of the dinosaur age still hanging on were dealt a critical and final blow some 150,000 years later. That timing lines up with the formation of the Chicxulub crater in the Yucatan from an estimated 6.2 mile wide asteroid.

"It’s quite likely both the volcanism and the asteroid were to blame for the ultimate mass extinction," University of Florida geochemist Andrea Dutton said in a release. "The Deccan Traps weakened the ecosystems before the asteroid slammed into the Earth— it’s consistent with an idea called the press-pulse hypothesis: a ‘one-two punch’ that proved devastating for life on Earth."